Microfluidics is an appealing method to study processes at rock pore scale such as oil recovery because of the similar size range. It also offers several advantages over the conventional core flooding methodology, for example, easy cleaning and reuse of the same porous network chips or the option to visually track the process. In this study, the effects of injection rate, flood volume, micromodel structure, initial brine saturation, aging, oil type, brine concentration, and composition are systematically investigated. The recovery process is evaluated based on a series of images taken during the experiment. The remaining crude oil saturation reaches a steady state after injection of a few pore volumes of the brine flood. The higher the injection rate, the higher the emulsification and agitation, leading to unstable displacement. Low salinity brine recovered more oil than the high salinity brine. Aging, initial brine saturation, and the presence of divalent ions in the flood led to a decrease in the oil recovery. Most of the tests in this study showed viscous fingering. The analysis of the experimental parameters allowed to develop a reliable and repeatable procedure for microfluidic water flooding. With the method in place, the enhanced oil recovery test developed based on different variables showed an increase of up to 2% of the original oil in place at the tertiary stage.
The major contaminant targeted during the treatment of the oilfield produced water is dispersed oil.The efficiency of most separation processes highly relies on the size of the droplets, which can be increased through coalescence. Crude oil has a complex and field-dependent composition, which can affect the interfacial properties of the drops, and consequently the merging process in different ways. This study focused on the development of microfluidic techniques for investigating coalescence between crude oil drops. The experiments were performed with six diluted crude oils and three neat oils, the latter in the presence of an oil-soluble surfactant. The composition of the water phase was systematically varied (pH, ionic composition, presence of dissolved components). In general, crude oil droplets coalesced more readily in lower or neutral pH. The addition of dissolved Fluka acids to the water phase had a unique effect on each crude oil, reflecting their composition.What is more, this effect was similar to the presence of water-soluble crude oil components in the aqueous phase. The pressure did not have a significant effect on the coalescence, which was explained by the lack of the lightest components (C1-C4) in the system. In summary, the results revealed several trends, however it was clear that the coalescence highly depended on the oil composition. This underlined the necessity for experimental methods, such as microfluidics, which allow for quick assessment of the stability of crude oil droplets.
Gas flotation is often used during treatment of the oilfield produced water. It relies on the generation of gas bubbles and their attachment to oil drops, for example, by forming an oil film on the surface of a gas bubble. In this paper, we present a microfluidic technique for investigating the attachment of crude oil drops to gas bubbles through the spreading mechanism. The developed method allowed us to systematically study the effect of the oil, water, and gas phases, where the investigated parameter was the amount of oil droplets attached to gas bubbles through spreading. The highest attachment efficiency was observed at low or neutral pH. By reducing the salinity, the electrostatic repulsion increased, which had a negative effect on the attachment. The presence of dissolved components stabilized the oil drops and gas bubbles, which decreased their attachment through spreading. Replacing nitrogen with methane improved the attractive interactions between bubbles and oil droplets, enhancing the attachment of oil. The results confirm the potential of microfluidics in studying bubble−droplet interactions, relevant for industrial processes.
Produced water originates from the crude oil production. It is a mixture of organic and inorganic compounds and its composition is highly oilfield-dependent. The present study was carried out to increase the understanding of the relations between the crude oil properties and the composition of the aqueous phase on the produced water quality. Brines with different compositions and pH levels were mixed with five crude oils. Initially, the physicochemical properties and composition of the crude oils were determined, while the quality of the synthetic produced water samples were described by parameters such as the total oil concentration and organic carbon, pH, the drop size distribution and the Sauter mean diameter. The characterization part revealed that crude oils fell into two categories: light and heavier oils. 2 Most parameters like density, viscosity, total acid number (TAN) or composition reflected this division. A similar pattern was sustained for the water quality analyses. Water produced with heavier crude oils generally contained higher concentration of emulsified oil with the biggest and most polydispersed droplets. Light oils had a tendency to create water-in-oil emulsion between the oil and water phase, which impeded the phase separation, resulting in less free water. The Sauter mean drop diameters increased with pH of the water phase. However, the presence of calcium at the highest pH decreased the droplet size and the amount of free water, compared to the brine without divalent ions, which is in agreement with the interfacial role of the naphthenic acids in the crude oil emulsions. The results showed the significance of both the water and oil composition on the quality of the produced water. This can lead to improved fundamental perception of the produced water treatment process.
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